Six days after the 114,500 tonne Costa Concordia capsized off the Italian coast, hopes of finding anyone alive on the partially submerged hulk have all but disappeared and the cold waters around the ship have become noticeably rougher.

One of the specialist diving crews said on Thursday that the available window could be as small as 12-24 hours although the chief spokesman of the rescue services denied that any deadline had been set and added the situation was still evolving.

Eleven people are known to have died out of more than 4,200 passengers and crew aboard when the ship struck a rock just metres from the shoreline, tearing a large gash in the side of the hull.

As many as 24 people are still unaccounted for. Two French passengers were identified among the dead on Thursday.